Zyzygie’s Mumbles and Rambles

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Thanks Ascent.

It worries me a little that we have designed and built weapons systems that are so dependent on operating in a pristine environment. A war environment is inevitably one of chaos and one helluva big mess.

I hope I'm wrong.
 

Junkers had designed the Ju 288 wing spars to be forged, taper and all, in giant forging presses. The big upsurge in German munitions production in 1942 came from investments in tooling and factories made years earlier.

Normally the German WW2 aircraft suspended their engines of magnesium forgings. The Designer of the Me 410 however fearful that the presses would become targets for bombs designed suspension frames that were welded. He happened to be a welding expert. (that was in Rudiger Kosins book "The German Fighter". ) Kosin was the aerodynacist for the Ar 234.

Arado actually made complete experimental wings for the Arado 234 out of cast magnesium. There was no spars or structure. Just a caste solid hollow wing that functioned as a fuel tank.
 

I think I saw a YouTube video of a engine core, may have been LEAP or PW1000G that had diverter valves that bypassed foreign objects at the intermediate compressor.
 
If I remember — it's been a few years — for a large bird, the engine just has to demonstrate an orderly shutdown, no fire, no shed parts, no over stressing the engine mounts. For smaller birds, they have to provide some fraction of full thrust. Military engines have different rules. It's also not unknown for companies to cheat; GE did so with the CF6 used on early DC-10s,with the result that a DC-10 lost all three engines on takeoff from LaGuardia
 

They'll probably be able to 3D print that sort of thing before too long.
 
Zyzygie said:
Now instead of metal pressing, why didn't the Germans invent 3D printing?

Gas turbine blades can be 3D printed | Engineers Australia
Click to expand...

There were programs in Germany during the Second World War to produce ceramic and cremet gas turbines blades as well as another to produce water cooled turbines. In 1947 Siemens obtained permission from the western allied powers to start building turbines again and in 1948 commissioned a stationary power gas turbine that ran of blast furnace gas at a steel works. It used the standard Jumo 004 compressor, a large ceramic vertical combustion chamber, ceramic turbine nozzles and a 5 stage water cooled turbine. Sometime after that the British allowed them to use nimonic and the this no longer necessary to develop this technology. Ceramics have always been viable but high end metals have always remained a step ahead. Water cooling is effective as well with staleness steel type blades, the cooling requirements are not onerous and one could use the wing leading edge, a steam radiator to generate some thrust. Aluminium blades work as well but they are so conductive massive cooling is required.

the problem with 3D printing has always been that the alloy grain structure is not as good as that obtained by other methods.

in WW2 the germans made their blades out of sheet metal whereas the british were casting them and then machining them.

Shortly after the war the British sent intelligence teams to investigate German engine development. The one to Germany was headed by Roy Fedden (Bristol Sleeve Valve chief engineer). He produced an article in Flight Global of his interview of BMWs Hermann Oestrich. Österlich mentions that one of the German mistakes was neglecting fuel control system design for jets. He also mentions that BMW was considering water cooled turbines.
 
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Koopernic said:
the problem with 3D printing has always been that the alloy grain structure is not as good as that obtained by other methods.
Click to expand...

It seems that with gas temperatures of 1250C, tensile loading of 10 tonnes and rotational speed of 13,000 rev/minute, the blade material must be of high quality.
 
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Koopernic said:
Österlich mentions that one of the German mistakes was neglecting fuel control system design for jets. He also mentions that BMW was considering water cooled turbines.
Click to expand...

Arguably a very big mistake was to not develop high temperature nickel alloys for use in gas turbines. Without that, the concept of the gas turbine was "a pie in the sky." Something that would be good to have, but frankly not going to happen.
"...The German industry had been aware that in any possible war, nickel would be one of the key metals in short supply. Consequently, even before the war, efforts had been made to develop alternatives and R&D on nickel-heavy alloys was curtailed: e.g. Krupp works did not introduce an improved Tinidur alloy with 60% instead of 30% Ni because of the anticipated shortage, even though the high temperature advantages were known (Meher-Homji 1997). One of the areas in which this awareness manifested itself was in superchargers, which were the first applications of hollow turbine blades: a BMW turbo-supercharger ran successfully at 900°C in 1938, using internally air-cooled blades..."
Early German gas turbine development

Air-cooled and ceramic blades were interesting and innovative, but not going to be practical given wartime conditions and shortages of time and resources.
 
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An interesting source on He-162

"...The call for a Volksjager (people's fighter) is an astonishing late-war accomplishment that went from drawing board to flight in only three months. This very hurried project (code-named "Salamander") managed to produce the Heinkel 162, "unique in the history of aviation as the only aircraft in which development, pre-production prototypes and main production lines were started almost simultaneously and proceeded in parallel." Curious in the design is the location of the jet engine, mounted on top of the fuselage directly above and behind the cockpit; this motivated the installation of a simple ejection seat, reflecting that the pilots were more highly valued than the aircraft itself."

"The aircraft itself was very effective as a fighter interceptor, equalling the Me-262. In some ways it was superior: "The BMW engine proved to be far less sensitive to throttle movements than those of the Me 262, though still prone to flameouts. This allowed the He 162 to be flown up to the limits of the pilot's confidence in the aircraft, unlike the Me 262 whose engines restricted much in the way of maneuvers." It was very fast and well-armed. However, it had a problem of having a very short flight time of 30 minutes, and many operational losses were due to running out of fuel."

"Despite its rapid development and excellent qualities, it was another case of too little too late for the Luftwaffe. The production program was planned to put out 4,000 aircraft per month, but only a few hundred were in fact produced because of the success of the Allied bombing campaign. Although a very few He-162s did see action over Germany in April 1944, the fighter essentially had no impact on the war..."

​
 
JUMO 004 Turbine Blading:


"Contrary to popular belief, the 004A was a fairly sound performer when premium steels were used, and early versions were known to achieve a 200-250 hour service life. However, the diversion of critical materials into U-boat production and other projects late in the war forced Junkers to produce the 004B model with only 1/3 of the high-grade steel that had been used in the 004A. It was to be a disastrous concession for the Me 262."

"The introduction of inferior metals compounded an already problematic situation with the turbine blade design. These blades were rigidly mounted, contributing to severe root stress relief problems. The weaker metals simply could not withstand this kind of abuse and regular compressor failures were an inevitable consequence."

Me 262 PROJECT TECHNICAL DATA
 
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